Class Function In Extension Converting to Self

Question

I'm trying to create an extension for loading UIView (and subclasses) from XIBs. The desire is to have the extension return the specific subclass of UIView. Here's what I have thus far:

extension UIView {

    class func instantiateNIB(name: String, bundle: NSBundle? = nil) -> UIView? {
        let nib = UINib(nibName: name, bundle: bundle)
        let views = nib.instantiateWithOwner(nil, options: nil)

        for view in views {
            if let match = view as? UIView {
                return match
            }
        }

        return nil
    }

}

Then:

let spinner: Spinner = Spinner.instantiateNIB("Spinner") as! Spinner
let rater: Rater = Rater.instantiateNIB("Rater") as! Rater

The issue is this method always returns a UIView that needs the forced down casting in a subsequent call. Is it possible to modify it to perform the downcast automatically? For example:

let spinner = Spinner.instantiateNIB(name: "Spinner")
let rater = Rater.instantiateNIB(name: "Rater")

score 1 · Accepted Answer · answered Sep 04 '15 at 02:23

Try this:

extension UIView {

    class func instantiateNIB(name: String, bundle: NSBundle? = nil) -> Self? {
        return instantiateNIB(self, name: name, bundle: bundle)
    }

    private class func instantiateNIB<T>(type: T.Type, name: String, bundle: NSBundle? = nil) -> T? {
        let nib = UINib(nibName: name, bundle: bundle)
        let views = nib.instantiateWithOwner(nil, options: nil)

        for view in views {
            if let match = view as? T {
                return match
            }
        }

        return nil
    }

}

Class Function In Extension Converting to Self

1 Answers1